Metal dies



Oct. 13, 1970 WALKEY ETAL 31,533,271

METAL DIES Filed July 6. 1967 3 Sheets-Sheet 1 HIEATING 26 SOURCE i Q. R

IN VENTORS GEORGE J. WALKEY FRANK N. A'DGATE By W Agent Oct. 13, 1970wAl-KEY ETAL 3,533,271

METAL DIES Filed July 6, 1967 3 Sheets-Sheet 2 W m W1 M I h MIN.

NEW :Wm...W W "W INVENTORS GEORGE J. WALKEY F|G f FRANK N. ADGATE AgentOct. 13, 1970 G.J. WALKEY ETAL METAL DIES- 5 Sheets-Sheet :5-

Filed July 6. 1967 FIG-2 INVENTORS GEORGE J. WALKEY FRANK N. ADGATEUnitcd States Patent Office 3,533,271 Patented Oct. 13, 1970 3,533,271METAL DIES George J. Walkey, Burbank, and Frank N. Adgate,

Granada Hills, Calif., assignors to Lockheed Aircraft Corporation,Burbank, Calif.

Filed July 6, 1967, Ser. No. 657,720 Int. Cl. B21k 5/20 US. Cl. 72-476 4Claims ABSTRACT OF THE DISCLOSURE A die and the method of fabricating itutilizing the technique of thermal spraying. A matrix of predeterminedstrength is initially cast over a pattern to a desired thickness. Afterthe matrix hardens it is separated from the pattern, heated, and a metalor other die material sprayed over its formed surface. The combinationis then cured and allowed to cool, causing the matrix, but not the die,to crack and facilitating easy separation. The resulting die shell maythen be filled with a mixture of reinforcing material and binder andheated, causing the binder to liquefy. Upon cooling the bindersolidifies around the reinforcing material, giving great structuralintegrity to the die shell and producing a tough, high temperature die.

BACKGROUND OF THE INVENTION The ever-increasing use of high strengthsubstances such as titanium in many of todays products has greatlyintensified the need for an inexpensive method of fabricating dies.Aircraft and spacecraft, for example, are requiring larger amounts ofhigh strength materials than ever before. However, because only a fewparts may be needed and produced from a single die, the conventional hotstamping process commonly used becomes prohibitively expensive.

Many industries have turned to other techniques such as the Shaw processor the Keller method to at least partially alleviate this high cost.

The Shaw process uses a conventional casting technique with a specialsand matrix manufactured from Bakelite and resin. While close tolerancesare obtainable by this process it is economically unsatisfactory in hightemperature applications with hard materials.

The Keller method, on the other hand, is a pantographic-like process andinitially entails the making of the finished article as a master. Amachine is then slaved, by conventional means such as a stylus bearingagainst the outer surface of the master, to produce the desired copies.While this method may be utilized for hard materials, it is very slow,comparatively expensive and completely unsuited for tracing complexshapes.

As a consequence of the various disadvantages of the above methods, oneapproach has been to fabricate dies by means of various thermal sprayprocess. These processes generally involve the deposition of a metalliclayer on a plaster casting to produce a die shell. The use of suchprocesses indeed offer several important advantages in that the timerequired to produce the die as Well as the finished article, is muchless than by normal maching methods. In addition, complexity of shape isnot an important factor as it is in the Keller method.

However, metal spray techniques in the past have been severely limitedto low strength, low temperature melting metals such as Zinc or tin. Onereason for this has been the natural tendency of the sprayed metal as itcooled to contact, such shrinkage causing it to separate from thepatterned surface. This tendency produced cracks and spalling,apparently due to the uneven thermal stresses produced in the metal whensprayed onto the pattern. Consequently, it has heretofore been verydifficult to spray an accurate negative or mold having sufficientstrength or rigidity for practical use.

While such dies are suitable for forming low strength materials and foroperating at low temperatures, they cannot be used to form strongmaterials at high temperatures. Thus, titanium, for example, which mustbe formed at a high-temperature because of its tendency to springback orreturn to its original shape, could not until now, be formed on a diemanufactured by the thermal spray method.

It is, therefore, a purpose of this invention to provide a method offabricating a strong, high temperature die wherein a substrate or matrixof predetermined strength is deposited upon a pattern to a desiredthickness. After being heated and cured, to remove excess water, thematrix is separated from the pattern and is again heated to atemperature compatible with that of the metal to be subsequentlydeposited thereon. The combination is thereafter placed in a preheatedoven and allowed to slowly cool, at which time, the substrate will crackbecause of its difierences in predetermined strength, thickness, andthermal coefiicient of expansion as compared with those of the metalliclayer. Upon having the matrix thoroughly removed from its surface, theresulting metal shell or die is filled with a selected mixture ofreinforcing material and binder and heated, causing the binder toliquefy. As the mixture cools, the binder hardens and adheres thereinforcing material to the die shell.

BRIEF DESCRIPTION OF THE DRAWING The procedure of the present .inventionas applied to the production of a die is illustrated by the accompanyingdrawing, wherein:

FIG. 1 is a perspective view of a heated die configuration manufacturedin accordance with the invention;

FIG. 2 is a longitudinal section through a mold pattern after thesubstrate or matrix has been deposited thereon;

FIG. 3 is the matrix of FIG. 2 after it has been removed from the moldpattern and a layer of die material deposited thereon;

FIG. 4 is similar to FIG. 1 and illustrates the die material separatedfrom the matrix with a mixture of reinforcing material and binder inreinforcing relationship therewith;

FIG. 5 illustrates an alternate embodiment of the matrix with a layer ofdie material deposited thereon;

FIG. 6 is the die material layer of FIG. 5 separated from the matrixwith a binder deposited thereon;

FIG. 7 is the die of FIG. 6 with additional layers of die materialdeposited thereon, and

FIG. 8 is an enlargement of the mixture of reinforcing material andbinder of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 14 and 8,there is depicted a mold 10 having a surface 12. dimensionally contouredto a desired configuration and smoothness. In contrast to the molds usedin prior art processes, particularly Where sintering procedures areused, mold 10 may be fabricated from an inexpensive material such asplastic, plaster or wood. This economy is possible since the mold 10 andthe surface 12 are not subject to deterioration as a result ofsubsequent spraying steps.

The surface 12 is first coated with a parting agent to provide a partingcoating 14. The function of the coating 14 is to facilitate removal ofthe molded refractory skeleton from the mold 10. In the practice of thisinvention, the parting agent may be applied in any suitable fashion suchas by spraying or pouring. Although several layers of wax material willfaciiltate the separation of the skeleton from the mold sprayed Teflon,molybdenum disulfide or lacquer may also be used as the parting agent.Once the mold 10 has been coated with a parting agent, an inorganicmatrix or substrate is deposited thereover and over the coated surface12 by conventional means such as spraying, ladling or the like. Theinorganic matrix 15 is fabricated from an aluminide or beryllide such asaluminum oxide or beryllium oxide or from a cement. The matrix 15 is ofsuch a strength, thickness and substance that it is compatible with diematerial 16 to be sprayed thereon at a subsequent time. It is of primaryimportance that the substance used for the matrix 15 be of a strengthsufiicient to withstand the heat during the preheating procedures andthe internal pressures of handling which are produced during theprocess. For high temperature applications and the ability to withstandinternal stresses, a high strength cement has been found to be generallysuperior to plaster of paris or dental plaster. (38) Holfmaster-43965Elec. 'Ptg.day 9/18/70 The resulting strength of the deposited matrix 15is a critical consideration since the matrix 15 must have a compressivestrength which is less than the yield strength of the die material 16which is subsequently deposited thereon. Were it otherwise, die 17 wouldcrack during the cooling process. After a predetermined thickness isreached, the matrix 15 is oven or air cured, depending upon the type ofdie 17 to be fabricated and the die material to be used.

Highly acceptable results have been obtained by providing a matrix 15 ofthe high strength cement commercially known as Glass-Rok cured in anoven at 300- 400 F. for a period of approximately two hours. The curingtime is, of course, dependent upon the characteristics of the specificmaterial being cured and the curing temperature, but it is required thatthe water contained within the matrix 15 be completely removed sinceduring the heating cycle any water remaining in the matrix 15 turns tosteam, forming internal bubbles, thereby cracking the matrix 15 ordeforming the matrix surface 18.

After the matrix 15 cools, it is separated from the mold 10, suchremoval being facilitated by cracking of mold 10 which usually occursduring the cooling cycle. If the mold 10 does not crack, it may beremoved from matrix 15 by use of conventional means (e.g., hammer andchisel). Upon being removed, the matrix 15 is ready to be preheated to atemperature compatible with the die material 16 to be subsequentlydeposited thereon. The die material 16 itself is usually a metal ormetal alloy but may comprise other types of inorganic materials such asplastic, cement or plaster. Thus, while a metallic material is referredto hereinafter, it is to be noted that this is for illustrative purposesonly. In addition, an organic which, upon being heated, becomes aninorganic (e.g. calcium lactate into calcium oxide), may be used.

In order to obtain such temperature compatibility of the matrix 15, itis required that the preheat temperature be approximately that whichresults in a 50% yield strength of the sprayed metal. While somelatitude may be taken with regard to this temperature, the above hasbeen found to be generally satisfactory. In handling aluminum materials,for example, a requirement exists that the temperature of the preheatedmatrix 15 be approximately 800 F., while in handling steel or steelalloys the heating requirement is approximately l500 F.

When the desired preheat temperature is reached, the die material 16 issprayed on the matrix 15 to form a die 17 of predetermined yieldstrength, and of thickness compatible with the compressive strength ofthe matrix 15. During the metal spraying process, the preheattemperature is maintained by conventional and suitable means such as agas burner or oxyactylene flame (not shown) until such time as thedesired thickness of the sprayed metal is achieved. Again it is to benoted that the matrix 15 must be sufficiently thin that its compressivestrength is less than the yield strength of the die 17. As an ex- 4ample, based upon the reported structural properties of a mild steel,such as S.A.E. 1010 (30,000 p.s.i. tensile strength at 1000 F.) and ahigh strength cement such as Glass-Rok (4,000 to 6,000 p.s.i.compressive strength), a cement matrix 15 having a thickness within theapproximate range of to has been found to fail under the compressiveload applied by the thermal contraction of a A" mild steel coating atroom temperature.

The matrix surface 18 need not be coated with a parting agent as taughtby the prior art of metal spraying since the matrix 15 will resistspalling on die surface 19 without the requirement of a coatingtherebetween because of the preheating of the matrix 15 and thepreselected strength of the materials used.

After the layer of die material 16 has been deposited upon the preheatedmatrix 15, the combination is placed in a preheated oven (not shown) andallowed to slowly cool for a length of time precalculated to result infailure of the matrix 15. The temperature of the preheated oven shouldbe approximately that to which the matrix 15 was heated prior to thedeposition of die material.

During the cooling process, the die 17 and the matrix 15 cool andcontract at different rates because of their different coefficients ofthermal expansion. The usual result is a severe cracking of the matrix15. However, as previously indicated, this cooling process does notalways cause the cracking of the matrix 15. In such case it can besubsequently removed by suitable conventional means, as by hammer andchisel or by grit blasting it with 40 mesh chilled iron grit at p.s.i. Aclean metallic surface has been produced by each of the noted removalmethods, no apparent damage to die surface 19 having resulted. The die17 can, by the aforementioned procedure, be produced to any thicknessdesired, but because of its shell-like configuration would be somewhatlimited in strength and thus substantially unsuited for high temperatureforming of high strength materials but could, however, be utilized forforming lower strength materials such as plastic and thin aluminumsheet.

Although under normal circumstances the matrix 15 cracks, it is to benoted that the materials used for the die 17 and the matrix 15 may bechosen of materials having nearly identical thermal coefiicients ofexpansion thereby contracting at almost the same rate. While under thesecircumstances neither material will crack during the cooling period,this procedure is generally very costly and is therefore economicallyunsatisfactory over the method previously discussed.

It is of course apparent that in performing the above steps dimensionalcontrol, surface hardness and other metallurgical properties of thematerials used for the matrix 15 and die 17 should be determined priorto the initiation of the process. This provides the fabricator with theability to predict and control critical dimensions required to assurethat the yield strength of the die 17 is greater than the compressivestrength of the matrix 15.

After the combination has cooled the matrix 15 is separated from the die17 and excess overspray, if any, is removed by conventional means suchas by sawing, grinding, or the like, until the desired finisheddimensions are obtained. Since the finished dimensions are unaffected byexcess overspray, it is not mandatory that it be removed. However, ithas been found beneficial in that a more compact, easier handling andlighter weight die can be achieved if the additional material isremoved.

When the desired finished dimensions have been achieved, a mixture ofbinder material 22 (FIG. 4) and reinforcing material 24 (the combinationbeing sometimes referred to as reinforcing mixture) such as epoxy resinand metal shot, respectively, are deposited by pouring, ladling or thelike, within a cavity formed in the die 17 opposite its surface 19. Theingredients of the reinforcing mixture are carefully chosen to providethe desired strength of the finished die 17 and in view of temperaturesinvolved in forming the material of the ultimate product for which thedie of this invention is provided. After this mixture has been depositedthe combination is oven heated to a temperature sufficient to liquefythe binder material 22 which, upon cooling, adheres the reinforcingmaterial 24 to the die 17, thereby forming one continuous, solid, diemass. If a hot forming die is desired to be fabricated, a heating membermay be located within the die 17 and surrounded by the reinforcingmixture. The heating member 20 may be of any conventional means such asa high resistance wire or heating rod electrically connected to aheating source 26 by wires 28 and 30 as best illustrated in FIG. 4. Theusage of a heating member 20 located within the die serves the dualpurpose of heating the reinforcing mixture, thereby eliminating therequirement for oven heating and also permits the finished die to beintegrally heated for the purpose of hot forming materials such astitanium. The temperature to which the reinforcing mixture is heatedshould approximate that to which the matrix 15 and die 17 werepreviously preheated. The binder material 22 is selected such that itwill liquefy at or near the preheat temperature and when cooled causethe reinforcing material 24 to adhere to the interior portion of the diesurface 19.

Referring to FIGS. 57, a modified embodiment of the present invention isdepicted wherein a matrix 15 having a surface 18 of dimensionallycontoured shape and smoothness has a die material 16 deposited thereon.The matrix .15 in the modified embodiment may be of standard compositionand for this purpose plaster of paris has been found to be generallysatisfactory. The die material 16 sprayed upon the contoured surface 18need not be heated in the modified embodiment since it has been foundthat preheat is required only when a thick coating of die material 16 isdeposited. In this regard coatings of inch and under do not require thedie material to be heated since the internal stress determines thenecessity for preheat and is a function of thickness. After the diematerial 16 has set, a fiber glass binder 22 is deposited over the diematerial 16 to a thickness of approximately /2 inch. After air curingfor about three and one-half hours at room temperature, copperreinforcing material 24 is deposited on the binder 22 at roomtemperature to a thickness of inch. Finally an additional layer of epoxyimpregnated fiber glass binder 22 is deposited over the copper layer. Bysuch construction a composite die 17 may be formed for many usefulpurposes, such as filament winding or lay up of plastic parts or for theforming of aluminum of thicknesses of .060 inch or less The followingexamples are generally illustrative of the process:

EXAMPLE 1 A wooden mold 10 of the character illustrated in FIG. 2 andhaving a desired dimensionally contoured surface 12 was coated with a.005 inch layer of paste wax to form a parting coating 14 over itssurface 12. An inorganic matrix 15 of high strength cement wasthereafter deposited at room temperature upon the waxed surface 12 untilthe matrix 15 was /2 inch thick. The matrix 15 was deposited by sprayingit over the surface 12 and was precalculated to be of a thinnesssufficient to crack during the subsequent cooling steps. The matrix 15was then oven cured at a temperature of 350 F. for two hours and themold 10 separated therefrom after it had cooled to room temperature. Thematrix 15 was next preheated to 1500 F. and S.A.E. 1010 steel sprayedthereon to a thickness of inch. Upon obtaining the desired thickness,the combination was placed in a preheated oven at 1500 F. and allowed tofurnace cool for a period of four hours. The matrix 15 cracked for thereasons previously enumerated and the die surface 19 was cleaned of theresidue matrix material by grit blasting with 40 mesh chilled iron gritat p.s.i. A heating rod 20 connected to a heat source 26 and a mixtureof 10% sodium silicate binder material 22 and iron shot reinforcingmaterial 24 were then placed within the cavity of the die 17 oppositethe die surface 19. The mixture was then heated to a temperature of 1500F. and allowed to air cool until it reached room temperature. This diewas found to be suitable for both cold and hot forming of titanium andother high strength materials at temperatures of 1450 F. and above.

EXAMPLE 2 A Wooden mold 10 having a desired dimensionally contouredsurface 12 was coated with molybdenum disulfide to form a partingcoating 14 of .004 inch thickness. An inorganic matrix 15 of berylliumoxide was then deposited upon the coating 14 to a thickness of A inch,air cured at a temperature of 350 F. and then allowed to cool for 24hours to room temperature. Upon cooling, the matrix 15 separated fromthe mold 10 and was then preheated to 800 F. Aluminum was thereaftersprayed on the matrix 15 while the matrix 15 was maintained at 800 F. bya gas burner. A metal die shell of a 17 /2 inch thickness in length wasformed and the combination thereafter placed in an oven preheated to 800F., the oven then being turned off and the die allowed to cool for fourhours. Upon removal of the die from the oven, the matrix 15 was found tobe cracked. The die surface 19 was cleaned by grit blasting with 40 meshiron grit at 80 p.s.i. A mixture of 5% epoxy resin binder material 22and chopped fiber glass reinforcing material 24 was then depositedwithin the die 17 opposite the die surface 19. The combination was thenoven cured at a temperature of 150 F. and subsequently allowed to aircool for a period of 24 hours. The die was found suitable for coldforming low strength metals.

EXAMPLE 3 A plastic mold 10 having a predetermined contoured surface 12was coated with molybdenum disulfide to a thickness of .002 inch to forma parting coating 14 over its surface 12. A plaster of paris matrix 15was then deposited, at room temperature, over the parting coating 14.The matrix 15 was then oven cured at a temperature of 350 F. for fourhours and thereafter removed from the mold 10. Aluminum was next sprayedover the matrix 15 to a thickness of inch. The matrix 15 and thealuminum were not preheated during this step since the resultantinternal stresses determine the preheating requirement and are afunction of the thickness of the material. Epoxy impregnated fiber glasswas then deposited over the aluminum at room temperature to a thicknessof /2 inch. The combination was then air cured for three and one-halfhours at room temperature. Upon reaching room temperature a 4; inchlayer of copper was deposited at room temperature on the fiber glass.The die 17 was then filled with epoxy impregnated fiber glassreinforcing material 24 and air cured for 3 /2 hours. The die was foundto be suitable for filament winding and forming aluminum of thickness of.060 inch or less.

EXAMPLE 4 A plastic mold 10 was coated with lacquer to form a partingcoating 14 of a thickness of .003 inch. Dental plaster was thendeposited on the coating 14 to a thickness of A inch and the combinationoven cured at 225 F. for two hours. The matrix 15 was then removed fromthe mold 10 and preheated to 800 F. Zinc was then sprayed at 300 F. uponthe matrix 15 to form the die 17. The layers were then allowed to coolto F. requiring two hours. After the combination had cooled the matrix15 was removed from the die surface 19 and a mixture of 10% plaster ofparis binder material 22 and 90% aluminum reinforcing material 24 wasdeposited within the die 17 opposite the die surface 19. The combinationwas then oven cured at 250 F. for three hours and allowed to air coolfor 24 hours, at which time room temperature was achieved. A die wasproduced suitable for forming plastics and filament winding.

EXAMPLE A wooden mold 10 was coated with a paste wax .004 inch thick. Amatrix composed of finely powdered portland cement was deposited on themold 10 to a thickness of inch and thereafter cured at a temperature of175 F. for four hours. That matrix 15 was removed from the mold 10 andthen sprayed with a /2 inch layer of copper at room temperature. Thematrix 15 was then removed from the copper die 17 by means of gritblasting and a Cerro-Bend deposited within the die 17 opposite and diesurface 19. Cerro-Bend is a well known low temperature melting (185 F.)alloy of bismuth and lead, used in die work, and is readily availablefrom a number of manufacturers. The mixture was then allowed to set forapproximately four hours producing a die suitable for forming plastics.

The products produced in relation to these examples, while suitable forthe indicated uses, may obviously be found readily acceptable for otherapplications as well.

The various features and advantages of the invention are thought to beclear from the foregoing description. Other advantages not specificallyenumerated will undoubtedly occur to those skilled in the art as well asother modifications of the preferred embodiment illustrated. Thefollowing claims measure the invention in a die as illustrated by theabove Examples 1, 3, 4 and 5, respectively.

We claim:

1. A die for cold and hot forming a high strength material attemperatures at and above 1450 F. and having a solid continuous massformed from (a) and (b) below and comprising in combination,

(a) a S.A.E. 1010 sprayed steel forming a shell and a die surfacethereon,

(b) a mixture formed of substantially 90% iron shot and 10% sodiumsilicate deposited in said shell and heated to a temperature of 1500 F.

the combination of (a) and (b) then being air cooled to produce saiddie.

2. A die for filament winding, and forming aluminum,

and the like, of .060 inch or less thickness, comprising in combination,

(a) sprayed aluminium forming a shell and a die surface thereon,

(b) epoxy impregnated fiber glass deposited at room temperature withinsaid shell, the combination of (a) and (b) then being air cooled at roomtemperature for approximately 3 /2 hours,

(0) a layer of copper deposited at room temperature on said fiber glass,and

(d) additional epoxy impregnated fiber glass filling said shell, beingair cured thereto, to produce said die.

3. A die for forming a plastic article and filament winding, comprisingin combination,

(a) sprayed zinc formed into a shell and a die surface thereon for saiddie at 300 F. and cooled to 100 F. in substantially 2 hours,

(b) a reinforcing material deposited Within said shell and formedsubstantially of aluminum and 10% plaster, said material and shell beingoven cured at substantially 250 F. for 3 hours,

the combination of (a) and (b) then being air cooled for substantially24 hours.

4. A die for forming plastics comprising in combination,

(a) a sprayed copper layer forming a die surface and shell for said die,

(b) a low temperature melting alloy of bismuth and lead deposited withinsaid shell,

the combination of said copper layer and alloy producing said die uponsetting for approximately 4 hours.

References Cited UNITED STATES PATENTS 1,835,916 11/1933 Ragsdale 76-1073,015,292 1/ 1962 Bridwell 72342 3,125,974 3/1964 Toulmin 761073,195,341 7/1965 Zunich 72475 3,422,663 1/1969 James et al. 76-107LOWELL A. LARSON, Primary Examiner US. Cl. X.R. 76-107

